In Julian Assange and The Fifth Estate, the actor has found his most challenging muse yet

"I was frightened," Benedict Cumberbatch says in a soft, thoughtful voice, over lunch on a rainy afternoon in New York City. He's not talking about the terrible act of violence he survived on a trip to South Africa a few years ago. Nor the daunting prospect of playing some of the world's most recognizable figures: Stephen Hawking, in a 2004 BBC movie that served as one of his early breaks, or notorious WikiLeaker Julian Assange in Bill Condon's The Fifth Estate, opening Oct. 18.

He's talking about privacy. "I was worried about being exposed," he says. It began in 2010, when his reinvention of Sherlock Holmes besotted legions of his countrymen  and, famously, the groups of countrywomen who called themselves "Cumberbitches" until he told InStyle U.K. that he was concerned "about what it says for feminism ... Cumberbabes might be better." When Sherlock's second season premiered on PBS, its ratings beat recent numbers of cult favorites like Mad Men, with Cumberbatch as its cerebral pinup. "Stepping into the populist limelight," he says, "has been quite crazy."